public class LinkedList {
    static class ListNode{//节点类 - 因为节点是链表的属性，所以用static来修饰
        //节点的成员
        public int val;
        public ListNode prev;
        public ListNode next;
        public ListNode(int val){
            this.val = val;
        }
    }
    public ListNode head;//头节点 - 不是每个节点都是头节点，它是链表的属性，所以定义在节点类外面
    public ListNode last;//尾节点 - 同头节点
    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = node;
            return;
        }
        head.prev = node;
        node.next = head;
        head = node;
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = node;
            return;
        }
        last.next = node;
        node.prev = last;
        last = node;
    }
    //在任意位置插入，假设第一个节点的下标为0
    public void addIndex(int index,int data){
        if(index < 0 || index > size()) {
            System.out.println("index不合法！");
            return;
        }
        if(index == 0) {
            addFirst(data);
            return;
        }
        if(index == size()) {
            addLast(data);
            return;
        }
        //cur拿到了index下标的节点的地址
        ListNode cur = head;
        while (index != 0) {
            cur = cur.next;
            index--;
        }
        ListNode node = new ListNode(data);
        node.prev = cur.prev;
        node.next = cur;
        cur.prev.next = node;
        cur.prev = node;
    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = head;
        while (cur != null){
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                if(cur == head){
                    head = head.next;
                    if(head == null){//只有一个元素
                        last = null;
                    }else {//有多个元素
                        head.prev = null;
                    }
                }else {
                    if(cur == last){//尾节点
                        last.prev.next = null;
                        last = last.prev;
                    }else {//中间节点
                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }
                }
                return;
            }
            cur = cur.next;
        }
    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                if(cur == head){
                    head = head.next;
                    if(head == null){
                        last = null;
                    }else {
                        head.prev = null;
                    }
                }else {
                    if(cur == last){//尾节点
                        last.prev.next = null;
                        last = last.prev;
                    }else {
                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }
                }
            }
            cur = cur.next;
        }
    }
    //得到单链表的长度
    public int size(){
        ListNode cur = head;
        int count = 0;
        while(cur != null){
            cur = cur.next;
            count++;
        }
        return count;
    }
    //打印链表内容
    public void display(){
        ListNode cur = head;
        while(cur != null){
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();//换行
    }
    //删除链表
    public void clear(){
        ListNode cur = head;
        while(cur != null){
            ListNode curNext = cur.next;
            cur.next = null;
            cur.prev = null;
            cur = curNext;
        }
        head = null;
        last = null;
    }
}
